Google Inc. says it will spend hundreds of millions of dollars to develop renewable energy as part of an ambitious plan to clean the environment and reduce the company's own power bill.

The Mountain View company said Tuesday that it will open its deep pockets to foster innovation in solar, wind and geothermal technology in the hopes of making green energy cheaper than power produced by burning coal.

To start the initiative, Google said that it will invest tens of millions of dollars in renewable power, spread over research and development and related investments, in 2008.

"Solar isn't currently cheaper than coal," Google co-founder Larry Page said in a conference call. "That's the point of this - to get it there."

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Google also hopes to license any technology spawned from the effort to other companies so that they, too, can reduce their reliance on more polluting forms of energy while saving money. Co-founder Sergey Brin raised the possibility that the fees will be a new source of revenue for his company, but insisted that the goal isn't to rake in big profit.

About 40 percent of the world's electricity comes from coal-fired power plants. Providing an affordable, cleaner alternative would go a long way in reducing pollution, particularly in China, where coal plants are proliferating.

In unveiling its plan, Google joins many companies and investors focused on clean energy, an area that is getting increasing attention amid high energy costs and concern about global warming. That list includes Wal-Mart, Cisco Systems and Hewlett-Packard. Google's financial contribution will be relatively minor when measured against overall investment on alternative energy.

Ron Pernick, co-founder of Clean Edge, an energy research company, said U.S. venture capital investment alone in clean energy was $2.4 billion, according to a joint study by Clean Edge and Nth Power, a venture capital firm.

Whether Google's money will fund anything new is unclear because the company announced few specifics. But Pernick said that Google's contribution is significant nonetheless, because it sets a clear goal.

"What they did today was to put a stake in the ground saying, 'Let's get renewable energy to be cost-competitive with coal,' " he said. "That's the differentiator that shows vision and commitment."

In general, Google said it will make investments and give grants to projects that show promise in developing energy at a cost below coal-fired power plants. Companies, universities and research and development labs will be eligible.

Google.org, Google's philanthropic arm, which will fund all the company's investment in outside companies, already is working with two partners in alternative energy.

ESolar, in Pasadena, designs solar thermal power plants. Makani Power, in Alameda, is working on wind power generated at high altitudes, a futuristic technology that potentially calls for turbines to be held aloft on kites or sails.

Executives from both startups were unavailable for comment. Larry Brilliant, who leads Google.org, declined to offer details about their cooperation.

Google's founders acknowledged that renewable energy is far more expensive than coal, which can cost 2 to 4 cents per kilowatt hour, depending on the country. Bill Weihl, who oversees green energy for Google, said that the cost of renewable energy will have to drop to 1 to 3 cents per kilowatt hour to make it competitive.

James Sweeney, a Stanford professor and director of the university'sPrecourt Institute for Energy Efficiency, said wind and geothermal power, under ideal conditions, are already close to Google's target price. However, solar power is several times more expensive than coal and would require significant innovation to become competitive.

Sweeney applauded Google's plans and said that it's almost irrelevant whether the company meets its goal. He said that the money will push innovation if it is well spent.

"If a large fraction goes to investing into companies that are being created anyway, then it's a big drop in a bucket," Sweeney said. "But if it's funding basic research, which isn't getting enough funding, then it's probably a significant force in moving this forward."

As part of its plan, Google intends to hire up to 30 engineers and energy experts. The plan is to generate one gigawatt of renewable energy, enough to power a city the size of San Francisco.

No deadline was announced. The company gave a vague timeline of years, not decades.

Potentially, the company could even operate power plants next to its data centers.

Google's founders have long been interested in energy efficiency and have played a big role in getting the company to go green. Last year the company said it would become carbon-neutral by the end of this year, meaning that it will be responsible for zero carbon emissions.

Relying on renewable energy would help bring Google closer to the goal. But in practice, it probably means the company will engage in buying "carbon offsets," the controversial practice of paying others to plant trees that then absorb carbon dioxide from the atmosphere.

Already, Google has built a solar panel installation at its headquarters that generates 1.6 megawatts, making it among the biggest corporate arrays in the country. In addition, the company has put out a request for proposals to fund up to $10 million in research and development of electric and hybrid cars.

Google's founders have taken some hits, however, for failing to practice what they preach by flying in a Boeing 767 that they own through a holding company. Brin answered the criticism Tuesday by emphasizing that he compensates for the pollution from the flights by buying carbon offsets.

Brin added that Google's interest in renewable energy won't distract the company from its main search and online advertising businesses. But he added that he doesn't want the company's focus to "preclude us from using some of our resources on more speculative areas, especially when they touch us."